UVB irradiation induces rapid changes in galanin, substance P and c-fos immunoreactivity in rat dorsal root ganglia and spinal cord

- UVB irradiation of rat hind paws will induce inflammation as reflected by an almost two-fold increase in skin blood flow after 24 h.
- UVB induced inflammation will change the expression of galanin, SP and c-fos in DRG, dorsal horn, lateral spinal nucleus and around the central canal.
- Galanin is down-regulated in DRG neurons and up-regulated in dorsal horn, lateral spinal nucleus and around the central canal.
- UVB induced inflammation can induce c-fos activity in spinal cord by itself.
- UVB induced inflammation will induce increase of immunoreactivity for galanin and SP in the lateral spinal nucleus.

Recent studies have shown that UVB irradiation induces primary and secondary hyperalgesia in rats and humans peaking about 24 h after UVB exposure. In the present study we investigated the changes in galanin, substance P and c-fos immunoreactivity in rat DRG and spinal cord at the L5 level 2-96 h after UVB irradiation. UVB irradiation of the heel area in rats almost increased the skin blood flow two-fold 24 h after irradiation as measured by laser Doppler technique. UVB irradiation induced a significant reduction of the proportion of galanin positive DRG neurons for all time points, except at 12 h. In the spinal cord, UVB irradiation induced increased immunoreactivity for galanin in the dorsal horn, the area around the central canal and interestingly also in the lateral spinal nucleus 12-96 h after exposure. For substance P the proportion of substance P positive neurons was unchanged but UVB irradiation induced increased substance P immunoreactivity in the dorsal part of the spinal cord 48 h after irradiation. UVB irradiation also induced c-fos immunoreactivity in the dorsal horn and the area around the central canal 24 and 48 h after exposure. This translational model of UVB irradiation will induce rapid changes of neuropeptides implicated in nociceptive signaling in areas known to be of importance for nociception in a time frame, about 24 h after exposure, where also neurophysiological alteration have been described in humans and rats.